Class 10 Science

# Human Eye and Colourful World

## NCERT Exemplar Problems

### MCQs Part 2

Question 8: Which of the following statements is correct regarding the propagation of light of different colours of white light in air?

1. Red light moves fastest
2. Blue light moves faster than green light
3. All the colours of white light move with the same speed
4. Yellow light moves with the mean speed as that of the red and violet light

Answer: (c) All the colours of white light move with the same speed

Explanation: Speed of light is constant in a given medium

Question 9: The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light

1. Is scattered the most by smoke or fog
2. Is scattered the least by smoke or fog
3. Is absorbed the most by smoke or fog
4. Moves fastest in air

Answer: (b) Is scattered the least by smoke or fog

Explanation: As you have seen in explanations to questions 7, the wavelength of red light is the maximum among all colours of visible spectrum. Due to this, red light is scattered the least by smoke or fog and is easily visible from a distance.

Question 10: Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?

1. Dispersion of light
2. Scattering of light
3. Total internal reflection of light
4. Reflection of light from the earth

Answer: (b) Scattering of light

Explanation: During morning and evening, light has to travel a longer distance compared to any other time of the day. While travelling a longer distance, colours at the blue end of the visible spectrum get scattered away. Due to this, only colours at the red end of the spectrum reach our eyes and the sun appears reddish at sunrise or sunset.

Question 11: The bluish colour of water in deep sea is due to

1. The presence of algae and other plants found in water
2. Reflection of sky in water
3. Scattering of light
4. Absorption of light by the sea

Answer: (c) Scattering of light

Question 12: When light rays enter the eye, most of the refraction occurs at the

1. Crystalline lens
2. Outer surface of the cornea
3. Iris
4. Pupil

Answer: (b) Outer surface of the cornea

Question 13: The focal length of the eye lens increases when eye muscles

1. Are relaxed and lens becomes thinner
2. Contract and lens becomes thicker
3. Are relaxed and lens becomes thicker
4. Contract and lens becomes thinner

Answer: (a) Are relaxed and lens becomes thinner

Explanation: When ciliary muscles are relaxed, then lens becomes thinner and its focal length increases. When ciliary muscles contract, then lens becomes thicker and its focal length decreases.

Question 14: Which of the following statements is correct?

1. A person with myopia can see distant objects clearly
2. A person with hypermetropia can see nearby objects clearly
3. A person with myopia can see nearby objects clearly
4. A person with hypermetropia cannot see distant objects clearly

Answer: (c) A person with myopia can see nearby objects clearly

Explanation: Myopia is also called far-sightedness in which a person cannot see distant object clearly, but can clearly see nearby object.